Recently, a disk device such as a magnetic disk device and an optical disk device is widely used as an external recording device and an image recording device of a computer. In the magnetic disk device, a rotatable magnetic disk and an actuator supporting a magnetic head are generally provided in an enclosure. In order to improve performance of the magnetic disk device, a method of filling the enclosure with low-density gas such as helium and reducing rotational resistance of the magnetic disk and the magnetic head is suggested.
In such a magnetic disk device, airtightness of an enclosure is improved by using an airtight enclosure formed by laser-welding a top cover to an enclosure base. For example, pulse irradiation is used as a laser irradiation method and the top cover is irradiated with a laser beam while laser output is repeatedly turned on and off. In such a magnetic disk device, it is required that time for laser welding is reduced and seal performance is further improved.